Many machines and equipment include chambers, or zones that are pressurized or evacuated during operation of the equipment. As discussed herein, a zone is equivalent to an enclosed volume. The remote zones may have flexible walls or rigid walls and, may be coupled or non-coupled to each other.
The coupling between the various zones can comprise volumetric coupling that occurs when the zone walls are flexible and one zone expands and pushes against another zone. Outlet coupling occurs if a vacuum pressure connected to the zones drifts, causes outlet flows to change and results in flows transitioning. Inlet coupling occurs when there is a significant in-rush of flow into a manifold resulting in a drop of line pressure (transient behavior) that affects all the other zones fed by the same source.
Chemical mechanical polishing (CMP) machines are examples of machines that include zones that are pressurized or evacuated during use. CMP is a method of planarizing substrates, particularly silicon wafers, as part of semiconductor manufacturing processes. Such substrates are generally formed by the sequential deposition of conductive, semiconductive or insulative layers, and subsequent etching of the layers to create circuitry features. As a series of layers are sequentially deposited and etched, the outer or uppermost surface of the substrate becomes increasingly non-planar. There is a need, therefore, to periodically planarize the substrate surface.
The planarization method typically requires that the substrate be mounted on a carrier or polishing head of a CMP machine. The exposed surface of the substrate is placed against a rotating polishing pad of the carrier head, and the carrier head provides a controllable pressure on the substrate to push it against the polishing pad. A polishing slurry, including at least one chemically-reactive agent and, in some cases, abrasive particles, is supplied to the surface of the rotating polishing pad.
Internal chambers or zones of a typical carrier head are formed at least in part by resilient bladders which expand upon the zones being pressurized and which contract upon a vacuum being created by evacuation within the zones. For example, pressurizing a zone in the carrier head can be used to press a substrate against a rotating polishing pad, while creating a vacuum in the zone can be used to provide suction for holding the substrate against the carrier head during transfer of the substrate to and from the polishing pad. The pressure in each zone can be controlled such that the polishing pad applies a desired force on the substrate held by the carrier head.
A pneumatic control system for controlling pressure within the remote zones of the carrier head can include flow control lines having pressure transducers and controllable valves. The flow control lines of the pneumatic control system may be connected to the zones of the carrier head through relatively long tubing, e.g., one meter or more. The pneumatic control system connects the zones of the carrier head to at least one vacuum source and at least one pressure source, and is appropriately connected to a computer that is programmed to receive measurements from the pressure transducer, and command the valves to alternatively connect the remote zones of the carrier head to the vacuum source and the pressure source and, thus, pneumatically power the carrier head.
One problem associated with the pneumatic control system of the prior art is that the system relies solely on the pressure measured by the transducers placed in the flow control lines of the pneumatic control system. The transducers can only measure the pressure in the system and not in the remotely connected zones of the carrier head. As a result, the control system assumes that the pressures in the pneumatic control system are the same as that in the remotely connected zones of the carrier head. Such is clearly not the case, however, when localized pressure transients occur in the pneumatic control system, which leads to severe degradation of system performance.
What is still desired, therefore, is a new and improved pressure control system and method, which can be used for, but is not limited to, pressurizing and evacuating remotely connected zones, such as the chambers of a CMP carrier head, and that compensates for pressure measurements taken in lines remotely connected to the zones. Preferably, the new and improved pneumatic control system can be used for pressurizing and evacuating a multi-zone system, wherein the zones possess rigid or flexible walls, and wherein the zones are coupled or non-coupled.